The replacement of a bone fragment missing in a lower jaw or its repair, for example following a tumor resection or of a severe trauma, or more simply the healing of a bone following an osteotomy performed to modify the bone anatomy, call upon several types of operation techniques.
One of these techniques, distraction osteogenesis, which is a surgical procedure used to reconstruct bone deficiencies or defects or to lengthen the bones of the human body, consists in placing a mechanical apparatus called distractor, whose role is to pull on the osseous callus resulting from the osteotomy in order to elongate it by a distance corresponding to the bone loss.
Whatever the organ concerned, this procedure is performed in several steps that can be broken down in the following manner. First, a surgical procedure is performed, which consists mainly in a sub-periosteal osteotomy in order to fracture the bone to be reconstituted and thus to divide it into at least two segments. After a latency period, these segments are gradually moved apart from one another by means of a distractor. A stabilization phase, in which the bone is allowed to consolidate, obviously precedes the removal of said distractor.
Several distraction osteogenesis techniques have already been successfully used in restoring interrupting substance loss (ISL) in the mandible, in the maxillary or in the malar bone, in particular in the case of ballistic traumas (for example following a firearm suicide attempt) of the face. Distraction osteogenesis enables the bone, gums and surrounding soft tissues to be reconstructed.
Several distractors corresponding to these various techniques for reconstructing loss of bone and of soft tissues of the lower face or middle face are thus already known in the prior art.
Patent application EP0770359, filed by the company Medicon, published on 2 May 1997, describes a mandibular distraction system implementing a first technique. A miniature screw jack, whose two extremities are fastened on each side of the osteogenic callus, exerts a traction on the latter, so as to ensure the new formation of a replacement bone tissue in its place. The whole device is entirely contained in the mouth cavity and the screw can be operated from the outside by a screwdriver type tool.
However, the apparatus remains bulky, notably the telescopic part, and it is impossible to place several of them on the same side of the mandible.
A slightly more compact device, constituted by a miniature double screw jack actuating two symmetric parts, which are integral to anchor points and are guided by two parallel rods, is described in international patent application WO 98/16163 in the name of M. Chin, published on 23 Apr. 1998. The whole apparatus is in a way a rectangle of variable length, whose extension is adjusted by the small jack.
The Chin device is capable of exerting considerable efforts and is particularly adapted for treating the rising branch of the lower jaw (ramus mandibularis), but its mechanical construction is rather complex.
International patent application WO 98/09577 in the name of M. Mommaerts, published on 12 Mar. 1998, pertains to a device still based on the same principle, but in yet another embodiment. The posterior extremity of the telescopic screw system rests directly on an insert placed in the rising branch of the lower jaw (ramus mandibularis), instead of being fastened onto a perforated bar which is common in implantology. The system is thus simpler and more compact, but it enables only the zones of the jaw located far at the rear to be treated.
The advantages of these jaw distractors reside in the fact that their intraoral application is simple and similar to osteosynthesis methods, that they are easy to activate and thus that they are accepted without problems by the patients.
However, a deficiency remains in their therapeutic indications since the prior art as described here above shows that none of these jaw distractors affords continuity in the effort or in the speed of distraction. All these devices operate in a discontinuous fashion, i.e. the bone to be reconstructed is subjected periodically to pulling so as to suddenly be displaced by several tenths of a millimeter each time, wherein the bone's spontaneous ability to regenerate will, in the hours that follow, fill the gap caused by the distractor's traction, and then the distraction operation is performed again by suddenly moving again the bone to be reconstructed by several tenths of a millimeter (according to a reference protocol, accepted by all practitioners, the traction on the bone to be reconstructed is classically performed on a daily or sometimes twice daily basis and this traction is on the order of 0.8 mm to 1 mm per day).
Known distractors furthermore have in most cases one or even two disadvantages: that of being very cumbersome and that of not directly allowing the reconstruction of the bone along a trajectory specific to the treated patient, notably when all or part of this trajectory is curved.
The intraoral jaw distractor according to the invention enables the above mentioned drawbacks to be overcome: the force it applies when striving to move the bone to be reconstructed is near continuous; it is compact, which is of particular importance when considering the intraoral character of such a mechanical device; furthermore, it can be constructed to reflect the patient, it can in a way be specific to each patient, whilst following the rectilinear parts and the curved parts that the bone should ideally follow after its reconstruction.
The geometry of the distractor according to the invention can thus be defined using computers preoperatively, taking into account: the substance loss following the operation or the trauma, the location of this substance loss and the volume of the remaining bone that can be used, and finally the image one wishes to restore in the patient.